The present invention relates to a process gas chromatographic system for analyzing a gas of interest by utilizing the difference in absorption between the gas and a filler filled in a column as a stationary phase.
In industrial processes such as a petrochemical process and an iron and steel production process, a process gas chromatographic system for analyzing components of process gases is employed to provide a sample gas extracted from a process line with an optimal condition required for analysis by means of a sample conditioner unit, supply this sample gas to an analyzer unit to separate the same into respective gas components for detection, and monitor process steps and perform various control operations based on the analysis results. FIG. 9 shows a conventional gas chromatographic system of this type. Reference numerals 1A and 1B denote process lines; 2, a sample conditioner unit; and 3, an analyzer unit. The process lines 1A and 1B, the sample conditioner unit 2, and the analyzer unit 3 constitute the gas chromatographic system. The sample conditioner unit 2 includes a vaporizer (not shown) for perfectly vaporizing heavy components of a sample gas SG to prevent its condensation, a filter (not shown) for removing dust from the sample gas SG, a rotor meter (not shown) for measuring the flow rates of the sample gas SG and a reference gas HG, needle valves (not shown) for adjusting the flow rates of the reference gas HG and the sample gas SG, and a selector switch (not shown) for selecting an appropriate flow path. These components in the sample conditioner unit 2 are built in a housing 4 and are connected to each other through piping. The analyzer unit 3 includes first and second series-connected columns 5 and 6, a sample valve 7, a back-flush valve 8, a detector 9, a pressure reducing valve (not shown), an electric unit 10, a constant temperature oven 11, and a heater 12. The constant temperature oven 11 accommodates the first and second columns 5 and 6, the sample valve 7, the back-flush valve 8, the detector 9, and the like such that they are kept at an optimal temperature for separation analysis of the sample gas SG by circulating air heated by the heater 12. The first column 5 consists of a packed column which has an inner diameter of about 1 mm to 4 mm and a length of about 0.5 m to 3 m and in which a stationary phase is filled. The first column 5 can efficiently separate low-boiling point components containing small amounts of carbon (C) at high speed. The second column 6 consists of a capillary column which has an inner diameter of about 0.1 mm to 4 mm and a length of about 0.5 m to 3 m and which has the inner wall surface coated with a liquid phase. The second column 6 cannot easily separate low-boiling point components containing small amounts of carbon but can efficiently separate high-boiling point components having large amounts of carbon at high speed. In an actual analysis, heavy components having large amounts of carbon (i.e., high-boiling point components) in the sample gas SG are discharged by the back-flush valve 8 and are not subjected to measurement to shorten the analysis cycle and protect the column from deterioration. The low-boiling point components having small amounts of carbon alone are separated by the first column 5 at high speed. When a range of gas components having large amounts of carbon is to be measured, the second column 6 separates gas components (light components) having small amounts of carbon within this range. The gas components separated by the first and second columns 5 and 6 are converted into electrical signals by the detector 9. These electrical signals are proportional to the concentrations of the respective gas components.
In the conventional gas chromatographic system having the above structure, however, the temperature distribution in the constant temperature oven 11 cannot be made perfectly uniform due to the number of spray ports of the sample gas SG and a carrier gas CG and the layout of components of the system. In addition, variations in temperature also occur. For these reasons, the components such as the columns 5 and 6 cannot be maintained under optimal temperature conditions, whereby the detected concentrations of components do not often coincide with the sample concentrations, which results in difficulties in achieving accurate measurements. For example, with the sample gas SG susceptible to liquefaction, the sample valve 7 and the back-flush valve 8 are preferably maintained at high temperatures, and the second column 6 is preferably free from variations in temperature so as to improve the separation performance.
In the conventional apparatus, a sample inlet portion between the sample conditioner unit 2 and the analyzer unit 3 is connected by a sample pipe 13. To prevent a sample gas from being cooled down during the transportation through the sample pipe 13, the sample pipe 13 is double structured and heated with steam or the like. For this reason, the piping structure is complicated, and a large number of parts are required. If the sample conditioner unit 2 is placed close to the analyzer unit 3, a piping operation becomes difficult. On the contrary, the sample conditioner unit 2 placed far from the analyzer unit 3 will cause a large temperature drop of the sample gas, which results in requiring more energy to maintain a constant temperature.
The electric unit 10 including an amplifier and a temperature controller, since located generally above the thermostat together with the heater 12, is adversely affected by heat from the constant temperature oven 11 and the heater 12, thus degrading reliability of the apparatus. Further, the structure, in which the sample valve 7, the first and second columns 5 and 6, the detector 9, and the like are connected to each other through piping and couplings inside the constant temperature oven 11, may cause problems such as a difficult maintenance operation of these components.